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Lutetium oxyorthosilicate Lu2SiO5 (LSO) and pyrosilicate Lu2Si2O7 (LPS) activated by Ce3+ or Pr3+ are known to be effective and fast scintillation materials for the detection of X-rays and γ-rays. Their performances can be further improved by co-doping with aliovalent ions. Herein, we investigate the Ce3+(Pr3+) → Ce4+(Pr4+) conversion and the formation of lattice defects stimulated by co-doping with Ca2+ and Al3+ in LSO and LPS powders prepared by the solid-state reaction process. The materials were studied by electron paramagnetic resonance (EPR), radioluminescence spectroscopy, and thermally stimulated luminescence (TSL), and scintillation decays were measured. EPR measurements of both LSO:Ce and LPS:Ce showed effective Ce3+ → Ce4+ conversions stimulated by Ca2+ co-doping, while the effect of Al3+ co-doping was less effective. In Pr-doped LSO and LPS, a similar Pr3+ → Pr4+ conversion was not detected by EPR, suggesting that the charge compensation of Al3+ and Ca2+ ions is realized via other impurities and/or lattice defects. X-ray irradiation of LPS creates hole centers attributed to a hole trapped in an oxygen ion in the neighborhood of Al3+ and Ca2+. These hole centers contribute to an intense TSL glow peak at 450–470 K. In contrast to LPS, only weak TSL peaks are detected in LSO and no hole centers are visible via EPR. The scintillation decay curves of both LSO and LPS show a bi-exponential decay with fast and slow component decay times of 10–13 ns and 30–36 ns, respectively. The decay time of the fast component shows a small (6–8%) decrease due to co-doping. [ABSTRACT FROM AUTHOR]

The influence of Mo on the electronic states and crystalline structure, as well as morphology, phase composition, luminescence, and defects in ZnO rods grown as free-standing nanoparticles, was studied using a variety of experimental techniques. Mo has almost no influence on the luminescence of the grown ZnO particles, whereas shallow donors are strongly affected in ZnO rods. Annealing in air causes exciton and defect-related bands to drop upon Mo doping level. The increase of the Mo doping level from 20 to 30% leads to the creation of dominating molybdates. This leads to a concomitant drop in the number of formed ZnO nanorods. [ABSTRACT FROM AUTHOR]

Erbium-doped Y3Al5O12 (YAG) single crystals grown using the micro-pulling-down technique were investigated. Three Er concentrations were chosen: 0.1, 0.3 and 1 at%. Er3+ electron paramagnetic resonance (EPR) spectra were measured in the ground and first excited states. The corresponding g tensors and 167Er hyperfine interaction were changing upon Er content indicating moderation of the Er-O bond length and/or Er local surrounding. Photoluminescence (PL) and radioluminescence (RL) spectra were complex, consisting of strongly overlapped typical Er3+ transitions. In addition, there were other broad PL band (3.1 eV) and RL band (3.95 eV) attributed to the F+ center and yttrium substituting for aluminum (YAl), respectively. The X-ray excited decay kinetics exhibited a decrease of the decay time of the YAl from hundreds of nanoseconds to nanoseconds upon Er doping level. This is discussed and explained considering EPR data. [ABSTRACT FROM AUTHOR]

Nanorods of erbium-doped zinc oxide (ZnO:Er) were fabricated using a hydrothermal method. One batch was prepared with and another one without constant ultraviolet (UV) irradiation applied during the growth. The nanorods were free-standing (FS) as well as deposited onto a fused silica glass substrate (GS). The goal was to study the atomistic aspects influencing the charge transport of ZnO nanoparticles, especially considering the differences between the FS and GS samples. We focused on the excitons; the intrinsic defects, such as zinc interstitials, zinc vacancies, and related shallow donors; and the conduction electrons. UV irradiation was applied for the first time during the ZnO:Er nanorod growth. This led to almost total exciton and zinc vacancy luminescence reduction, and the number of shallow donors was strongly suppressed in the GS samples. The effect was much less pronounced in the FS rods. Moreover, the exciton emission remained unchanged there. At the same time, the Er3+ content was decreased in the FS particles grown under constant UV irradiation while Er3+ was not detected in the GS particles at all. These phenomena are explained. [ABSTRACT FROM AUTHOR]

Cesium lead bromide (CsPbBr 3 , CPB) powder formed by micro-, nanocrystals (MC, NC) and quantum dots (QD) was synthesized as free-standing and polystyrene covered. Luminescence was multicomponent, in general, ranging from below 1.9 eV up to about 2.6 eV. The ultrafast decay kinetics exhibited strong decay time component with the value of 260 ps. Electron paramagnetic resonance (EPR) revealed surface defects like O 2 − and some spin transitions most likely originating from some complex defect, supposedly F-V k (H) dimer center under the constant ultraviolet (UV) light irradiation at the temperature T = 10 K. The thermal release of the electrons from the O 2 − center was correlated with the 117 K thermally stimulated luminescence (TSL) peak. Coating with polystyrene resulted in the about doubly increased decay time of luminescence. The O 2 − and F-V k (H) EPR resonances were not observed as well. The TSL peak which might be ascribed to the O 2 − was not clearly detected anymore. The glow curve was composed of one very broad peak typical for the amorphous materials. At the same time, the polystyrene prevented the MCs creation. The existence of charge/energy transfer between the CPB and polystyrene due to the chemical bonding was assumed and confirmed also by calculations. [Display omitted] • EPR, TSL and RL study of charge trapping and luminescence in CsPbBr 3. • Charge/energy transfer was detected. • O 2 − -related electron trapping center was revealed in these crystals. • TSL peak was correlated to the release of electrons from the O 2 − surface center. • Complex bromine vacancy-related charge trapping center was observed. [ABSTRACT FROM AUTHOR]

The development of ultrafast scintillators is critical to the GHz X‐ray and time‐of‐flight (TOF) imaging techniques. Low‐dimensional silver‐based halides have emerged as promising candidates due to high radioluminescence efficiency and ultrafast decay time. However, the ultrafast scintillation mechanism in silver‐based halides, such as Rb2AgBr3 (RAB), remains controversial. Here, the study reveals the origin of ultrafast scintillation timing response in melt‐grown RAB bulk crystals. The RAB shows light‐yellow emission with a photoluminescence quantum yield (PLQY) of 13.9%. Under the picosecond (ps) pulse X‐ray irradiation, RAB has an ultrafast decay time of 3.2 ns that accounts for 40.5% of the total emitted light. The light yield is estimated as 3100 photons MeV−1 under 22Na irradiation. Based on the temperature‐dependent radioluminescence (RL) spectroscopy, electron paramagnetic resonance (EPR) spectroscopy, and spectrally resolved thermally‐stimulated luminescence (TSL) glow curves, it is confirmed that the bromine vacancy as the F‐center is the origin of the ultrafast scintillation component. These findings provide elaborated and fundamental insights into the ultrafast luminescent mechanisms of low‐dimensional silver‐based halides, thereby opening up new design horizons in the development of ultrafast scintillators. [ABSTRACT FROM AUTHOR]

[Display omitted] • Electron and hole trapping centers were observed in the molybdenum doped zinc oxide rods. • Electron trapping centers were mostly molybdenum-based. • Holes were trapped at oxygen complexes. • Exciton- and defect-related emission bands appear suppressed after X-ray irradiation. • Zinc vacancies participated in the charge trapping processes. Peculiarities of the point defects creation under X-ray irradiation and the influence of Mo doping in ZnO powders of nano- and microrods fabricated by the hydrothermal growth method (as-grown and annealed in air) were studied in detail. Correlated experiments of X-ray diffraction, X-ray photoelectron spectroscopy, electron paramagnetic resonance, photo- and radioluminescence as well as thermally stimulated luminescence allowed us to trace the effect of the molybdenum inclusion on the phase purity of synthesized materials and the role of Mo in the creation of X-ray induced point defects. Oxygen-based hole trapping centers (most probably involving interstitial oxygen) as well as Mo5+-based electron trapping centers were observed and their thermal stabilities were studied. Some amount of the hole trapping centers seemed to be directly connected with the creation of Mo5+. Zinc vacancies and the Mo5+ centers up to some extent were assumed to act as recombination centers for the holes released from the hole trapping centers. The X-ray irradiation also affects the luminescence properties of the ZnO:Mo samples – the intensity of the luminescence bands in general becomes weaker. [ABSTRACT FROM AUTHOR]

Glass ceramics in the form of MI 2 :Eu crystalline particles grown in MO-B 2 O 3 glass (M = Ca, Sr, Ba) through recrystallization from the alloyed melt were fabricated. Eu2+ ions were detected in the CaI 2 and SrI 2 crystalline particles (not in the BaI 2) inside the corresponding glasses. Some amount of Eu2+ centers are expected to originate from the MO-B 2 O 3 glass hosts as well. This was confirmed by correlated electron paramagnetic resonance (EPR), photo- and radioluminescence (PL, RL) measurements. Peculiarities of the Eu2+ distribution and incorporation into the glass ceramics samples as well as charge and energy transfer properties are discussed in detail. Optimal conditions leading to the enhancement of the Eu2+ emission from the CaI 2 and SrI 2 crystallites inside the glasses were determined. [ABSTRACT FROM AUTHOR]